Snowshoe hare populations in woodlot habitat

1978 ◽  
Vol 56 (5) ◽  
pp. 1071-1080 ◽  
Author(s):  
Lamar A. Windberg ◽  
Lloyd B. Keith
Keyword(s):  
Population Dynamics ◽  
Population Decline ◽  
Lepus Americanus ◽  
Snowshoe Hare ◽  
Population Densities ◽  
Population Growth Rates ◽  
Food Shortages ◽  
Annual Population ◽  
Reproductive Rates ◽  
Lower Population

Snowshoe hare (Lepus americanus) population dynamics were monitored on six woodlots totaling 33 ha in an agricultural area near Westlock, Alberta, from May 1970 to May 1974. Numerical trends in woodlot and nearby forest hare populations at Rochester were similar, but densities were consistently lower in woodlot habitat until the final stages of a general population decline. Annual reproductive rates were greater in woodlot populations in 1971 (11.2 vs. 9.1 young per adult female) and 1973(11.1 vs. 7.4); and similar to forest populations in 1970 and 1972. Consistently low rates of 1st-year survival (4 to 7%) in woodlot hare populations resulted in lower annual population growth rates and hence lower population densities. Browsing-intensity surveys indicated that both forest and woodlot hare populations encountered overwinter food shortages. In addition, woodlot hare populations may have suffered higher rates of predation.

The role of dispersal in the population dynamics of snowshoe hares

1985 ◽  
Vol 63 (1) ◽  
pp. 106-115 ◽  
Author(s):  
Stan Boutin ◽  
B. S. Gilbert ◽  
Charles J. Krebs ◽  
A. R. E. Sinclair ◽  
J. N. M. Smith
Keyword(s):  
Population Dynamics ◽  
Small Mammals ◽  
Lepus Americanus ◽  
Population Increase ◽  
Dispersal Rate ◽  
Population Densities ◽  
Control Grid ◽  
Snowshoe Hares ◽  
Kluane Lake

We monitored dispersal of snowshoe hares (Lepus americanus) at Kluane Lake, Yukon, during a population increase, peak, and decline. Dispersal was measured by recording the number of immigrants to a removal grid and by tracking radiocollared individuals. The observed decline was not due to dispersal, as a maximum of 28% of all losses of radiocollared animals was due to dispersal. Dispersal rate (as measured by number of immigrants to the removal grid per individual on the control grid) was negatively correlated (−0.51, P < 0.01) with the rate of population increase. Highest dispersal rates occurred in the winters when hare populations were at peak and early decline densities. Dispersers at this time were lighter in weight than residents. We discuss our results in light of current hypotheses attempting to explain dispersal in cyclic small mammals and conclude that our results are consistent with the hypothesis that food shortage is responsible for increased rates of dispersal at peak population densities Comparison of dispersal, as monitored by radiotelemetry, versus immigration to a removal grid, suggests that removal grids overestimate dispersal, particularly at high densities when removal grids may attract animals because food supplies are relatively favorable there.

Experimental analyses of dispersal in snowshoe hare populations

1976 ◽  
Vol 54 (12) ◽  
pp. 2061-2081 ◽  
Author(s):  
Lamar A. Windberg ◽  
Lloyd B. Keith
Keyword(s):  
Lepus Americanus ◽  
Snowshoe Hare ◽  
Lower Body ◽  
Population Densities ◽  
Population Response ◽  
Partial Removal ◽  
Resident Population ◽  
Body Weights ◽  
Sex Ratio Imbalance ◽  
Hare Population

Dispersal was investigated in snowshoe hare (Lepus americanus) populations near Rochester, Alberta, from May 1970 to May 1974. Ingressing hares (dispersers) were removed every 3 to 4 weeks after removal of the initial resident population from an 11.3-ha study area. Dispersal into this vacant habitat occurred during all seasons of each year. The highest rates of ingress were recorded during the winter of peak population densities (1970–1971). There was a higher proportion of short-yearlings among ingressing hares than among residents. During two winters of known food shortage (1970–1971 and 1971–1972) dispersing hares had lower body weights than residents. Lighter adrenals and a higher incidence of scarring were also found among ingressing hares during winter 1970–1971.During winter 1971–1972 the resident hare population was removed from another area. Comparable recapture rates between marked immigrants on this area and hares on unmanipulated study areas indicated that ingressing individuals had settled in the vacant habitat.Hare population response to sex-ratio imbalance, created by partial removal of each sex on different areas, was studied during 1970 and 1971. Pregnancy rates declined significantly only on the male-removal area. Movements by adults during the breeding season and by predominantly juveniles over winter tended toward rebalancing population sex ratios.

Mammal population cycles: evidence for intrinsic differences during snowshoe hare cycles

2003 ◽  
Vol 81 (2) ◽  
pp. 216-220 ◽  
Author(s):  
A R.E Sinclair ◽  
Dennis Chitty ◽  
Carol I Stefan ◽  
Charles J Krebs
Keyword(s):  
Reproductive Output ◽  
Population Cycles ◽  
Food Shortage ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Population Densities ◽  
Northern Latitudes ◽  
Snowshoe Hares ◽  
Reproductive Rates ◽  
High Phase

Some mammals in high northern latitudes show regular population cycles. In snowshoe hares (Lepus americanus), these occur every 9–10 years. One hypothesis proposes extrinsic causes such as food shortage or predation. The other proposes intrinsic causes through different morphs that alternate between different phases of the cycle. The morphs should differ in behaviour or physiology. This hypothesis predicts that animal lineages bred from high and low phases of the population cycle should differ in reproduction and survivorship. In a 16-year breeding program, lineages of purebred high-phase female hares had reduced reproductive rates relative to those of purebred low-phase females, resulting in extinction of high-phase lineages. Reproductive output declined with age in high- but not low-phase animals. These lineages also differed in longevity and senescence. These results are consistent with the intrinsic hypothesis and suggest a mechanism for alternating population densities that could work synergistically with extrinsic causes like predation and food shortage.

Effects of harvest and climate on population dynamics of northern bobwhites in south Florida

2011 ◽  
Vol 38 (5) ◽  
pp. 396 ◽  
Author(s):  
Virginie Rolland ◽  
Jeffrey A. Hostetler ◽  
Tommy C. Hines ◽  
Fred A. Johnson ◽  
H. Franklin Percival ◽  
...  
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Population Growth ◽  
Population Growth Rate ◽  
Population Decline ◽  
South Florida ◽  
Winter Survival ◽  
Demographic Parameters ◽  
Population Growth Rates ◽  
Annual Changes

Context Hunting-related (hereafter harvest) mortality is assumed to be compensatory in many exploited species. However, when harvest mortality is additive, hunting can lead to population declines, especially on public land where hunting pressure can be intense. Recent studies indicate that excessive hunting may have contributed to the decline of a northern bobwhite (Colinus virginianus) population in south Florida. Aims This study aimed to estimate population growth rates to determine potential and actual contribution of vital rates to annual changes in population growth rates, and to evaluate the role of harvest and climatic variables on bobwhite population decline. Methods We used demographic parameters estimated from a six-year study to parameterise population matrix models and conduct prospective and retrospective perturbation analyses. Key results The stochastic population growth rate (λS = 0.144) was proportionally more sensitive to adult winter survival and survival of fledglings, nests and broods from first nesting attempts; the same variables were primarily responsible for annual changes in population growth rate. Demographic parameters associated with second nesting attempts made virtually no contribution to population growth rate. All harvest scenarios consistently revealed a substantial impact of harvest on bobwhite population dynamics. If the lowest harvest level recorded in the study period (i.e. 0.08 birds harvested per day per km2 in 2008) was applied, λS would increase by 32.1%. Winter temperatures and precipitation negatively affected winter survival, and precipitation acted synergistically with harvest in affecting winter survival. Conclusions Our results suggest that reduction in winter survival due to overharvest has been an important cause of the decline in our study population, but that climatic factors might have also played a role. Thus, for management actions to be effective, assessing the contribution of primary (e.g. harvesting) but also secondary factors (e.g. climate) to population decline may be necessary. Implications Reducing hunting pressure would be necessary for the recovery of the bobwhite population at our study site. In addition, an adaptive harvest management strategy that considers weather conditions in setting harvest quota would help reverse the population decline further.

Influence of rainfall on population dynamics and survival of a threatened rodent (Pseudomys novaehollandiae) under a drying climate in coastal woodlands of south-eastern Australia

2017 ◽  
Vol 65 (1) ◽  
pp. 60 ◽  
Author(s):  
Mandy Lock ◽  
Barbara A. Wilson
Keyword(s):  
Population Dynamics ◽  
Population Decline ◽  
Resource Depletion ◽  
Mammal Species ◽  
Eastern Australia ◽  
Apparent Decrease ◽  
Mediterranean Systems ◽  
Precipitous Decline ◽  
Breeding Seasons ◽  
Successional Vegetation

In Mediterranean systems, such as south-east Australia, predictions of climate change including lower rainfall and extended drought, threaten vulnerable mammal species. We investigated the relationship between rainfall and population dynamics for a native rodent at risk of extinction, the New Holland mouse (Pseudomys novaehollandiae). In the eastern Otways, the species was significantly influenced by rainfall, exhibiting a population irruption (15–20 individuals ha–1) following six years of above-average rainfall and a precipitous decline to site extinction during subsequent drought. The decline was predominantly related to loss of adults before and during breeding seasons, together with an apparent decrease in juvenile survival. Population abundance was positively correlated with a rainfall lag of 0–9 months. We propose that the response of this omnivore to high rainfall was mediated through increased productivity and that rainfall decline resulted in resource depletion and population decline. Under a drying climate the direct impacts of rainfall decline will continue. However management of other threats may increase the species’ resilience. Burning to provide optimal successional vegetation, protection of refugia, and predator control are priorities. However, burning should be avoided during drought, as the likelihood of local extinctions is substantial.

Effects of crop sequence and rainfall on population dynamics of Fusarium solani f.sp. phaseoli in soil

1992 ◽  
Vol 70 (10) ◽  
pp. 2005-2008 ◽  
Author(s):  
Robert Hall ◽  
Lana Gay Phillips
Keyword(s):  
Population Dynamics ◽  
Phaseolus Vulgaris ◽  
Population Density ◽  
Fusarium Solani ◽  
Population Densities ◽  
Total Rainfall ◽  
Colony Forming Units ◽  
Bean Crop ◽  
Previous Summer ◽  
Crop Sequence

Evidence is presented that population dynamics of Fusarium solani f.sp. phaseoli in soil depend on the effects of crop sequence and rainfall on parasitic activities of the pathogen. In a rotation trial started in 1978 and conducted over 14 years, population densities (colony-forming units/g) of the fungus in soil remained below 50 in treatments (fallow, repeated corn, repeated soybean) where the preferred host plant (common bean, Phaseolus vulgaris) was not grown. Where bean was grown every 3rd year or every year, population densities reached 475 and 660, respectively, by 1984. Thereafter, population densities of the fungus fluctuated widely from year to year in both rotation and repeated bean treatments. In the rotation treatment, peaks in population density of the pathogen coincided with the years of bean production. In repeated bean plots between 1985 and 1991, population density of the fungus in June was significantly correlated (r = 0.77, p = 0.04) with total rainfall received during the previous summer (June–August). It is postulated that higher rainfall during the growing season of the bean crop stimulated root growth and root infection, leading to the accumulation of higher levels of potential inoculum in infected tissue and the release of higher levels of inoculum into the soil by the following June. Key words: Fusarium solani f.sp. phaseoli, bean, Phaseolus vulgaris, rainfall, crop rotation.

Population densities and conservation assessments for three species of chameleons in the Toliara region of south-western Madagascar

2009 ◽  
Vol 30 (3) ◽  
pp. 341-350 ◽  
Author(s):  
Laza Andriamandimbiarisoa ◽  
Christopher Raxworthy ◽  
Kristopher Karsten ◽  
Stanley Fox
Keyword(s):  
Protected Areas ◽  
Conservation Priority ◽  
Population Densities ◽  
Pet Trade ◽  
Anthropogenic Habitats ◽  
Spread F ◽  
Illegal Harvesting ◽  
High Conservation ◽  
Conservation Assessments ◽  
Lower Population

AbstractMadagascar is a high conservation priority. Rainforests receive most of the focus, but the dry deciduous and spiny forests of south-western Madagascar house many endemics, are under high deforestation pressure, and remain largely unprotected. Charismatic vertebrates, like chameleons, face a secondary threat: harvesting for the commercial pet trade. Six chameleons inhabit the arid southwest near Toliara: Furcifer antimena, F. belalandaensis, F. labordi, F. lateralis, F. oustaleti, and F. verrucosus. We measured population densities of three of those species. Furcifer verrucosus has a large distribution, was dense (97.7 ha–1; 95% CI = 60.2-158.6), and inhabited forests and anthropogenic habitats. Furcifer labordi was much less dense (30.8 ha–1; 13.4-70.9), has a restricted range, and has a unique life history that makes it susceptible to perturbations from deforestation or illegal harvesting. Furcifer antimena was the least dense (17.0 ha–1; 9.3-30.9) and has an even smaller distribution range. We lack density data for F. lateralis, but this species was abundant in anthropogenic habitats. Within their respective ranges, there are currently no protected areas for F. antimena and only few for F. labordi; these two species are far less abundant than the more widely spread F. verrucosus. We recommend that high conservation priority be focused on F. antimena and the southern populations of F. labordi due to their restricted distributions, susceptibility to extirpation, lower population densities, and lack of formal protection. Establishing protected areas in the Ranobe region and north of the Fiherenana River, in the Belalanda region, would help protect important populations of these vulnerable species.

scholarly journals Northern Goshawk, Accipiter gentilis, Exploits a Beagle Hound, Canis familiaris, as a "Beater" to Catch a Snowshoe Hare, Lepus americanus

2007 ◽  
Vol 121 (3) ◽  
pp. 329
Author(s):  
John T. Neville
Keyword(s):  
Canis Familiaris ◽  
First Record ◽  
Lepus Americanus ◽  
Accipiter Gentilis ◽  
Snowshoe Hare ◽  
Northern Goshawk

During a winter Snowshoe Hare (Lepus americanus) hunt with a beagle hound (Canis familiaris), I observed an adult Northern Goshawk (Accipiter gentilis) exploiting the running, barking hound as a “beater” and use strategic locations for attacks. The hawk made three attacks on a hare being pursued by the hound, and subsequently caught and killed it. To my knowledge, this report represents the first record of a Northern Goshawk using this behavior to capture prey.

scholarly journals Interannual variation in the epibenthic megafauna at the shallowest station of the HAUSGARTEN observatory (79° N, 6° E)

2012 ◽  
Vol 9 (12) ◽  
pp. 18039-18081 ◽  
Author(s):  
K. S. Meyer ◽  
M. Bergmann ◽  
T. Soltwedel
Keyword(s):  
Population Dynamics ◽  
Deep Sea ◽  
Interannual Variation ◽  
Suspension Feeding ◽  
Fram Strait ◽  
Population Densities ◽  
Camera System ◽  
Sea Floor ◽  
Time Period ◽  
Food Input

Abstract. Epibenthic megafauna play an important role in the deep-sea environment and contribute significantly to benthic biomass, but their population dynamics are still understudied. We used a towed deep-sea camera system to assess the population densities of epibenthic megafauna in 2002, 2007 and 2012 at the shallowest station (HG I, ~ 1300 m) of the deep-sea observatory HAUSGARTEN, in the eastern Fram Strait. Our results indicate that the overall density of megafauna was significantly lower in 2007 than in 2002, but was significantly higher in 2012, resulting in overall greater megafaunal density in 2012. Different species showed different patterns in population density, but the relative proportions of predator/scavengers and suspension-feeding individuals were both higher in 2012. Variations in megafaunal densities and proportions are likely due to variation in food input to the sea floor, which decreased slightly in the years preceding 2007 and was greatly elevated in the years preceding 2012. Both average evenness and diversity increased over the time period studied, which indicates that HG I may be food-limited and subject to bottom-up control. The varying dynamics of different species may have been caused by differential capacities of populations to respond to increased food input through either recruitment or migration.

scholarly journals Separating the effects of climate, bycatch, predation and harvesting on tītī (Ardenna grisea) population dynamics in New Zealand: A model-based assessment

PLoS ONE ◽  
2020 ◽  
Vol 15 (12) ◽  
pp. e0243794
Author(s):  
Sam McKechnie ◽  
David Fletcher ◽  
Jamie Newman ◽  
Corey Bragg ◽  
Peter W. Dillingham ◽  
...  
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Southern Oscillation ◽  
Population Decline ◽  
Management Strategies ◽  
Model Averaging ◽  
Adult Survival ◽  
Enso Events ◽  
Introduced Predators ◽  
Best Fitting

A suite of factors may have contributed to declines in the tītī (sooty shearwater; Ardenna grisea) population in the New Zealand region since at least the 1960s. Recent estimation of the magnitude of most sources of non-natural mortality has presented the opportunity to quantitatively assess the relative importance of these factors. We fit a range of population dynamics models to a time-series of relative abundance data from 1976 until 2005, with the various sources of mortality being modelled at the appropriate part of the life-cycle. We present estimates of effects obtained from the best-fitting model and using model averaging. The best-fitting models explained much of the variation in the abundance index when survival and fecundity were linked to the Southern Oscillation Index, with strong decreases in adult survival, juvenile survival and fecundity being related to El Niño-Southern Oscillation (ENSO) events. Predation by introduced animals, harvesting by humans, and bycatch in fisheries also appear to have contributed to the population decline. It is envisioned that the best-fitting models will form the basis for quantitative assessments of competing management strategies. Our analysis suggests that sustainability of the New Zealand tītī population will be most influenced by climate, in particular by how climate change will affect the frequency and intensity of ENSO events in the future. Removal of the effects of both depredation by introduced predators and harvesting by humans is likely to have fewer benefits for the population than alleviating climate effects.

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